1. Field of the Invention
The present invention relates to mechanical switches and, more particularly, to a mechanical switch that reduces the effect of contact resistance.
2. Description of the Related Art
A switch is a well known electrical device that provides a low-impedance electrical pathway when the switch is “closed,” and a high-impedance electrical pathway when the switch is “opened.” A mechanical switch is a type of switch where the low-impedance electrical pathway is formed by physically bringing two electrical contacts together, and the high-impedance electrical pathway is formed by physically separating the two electrical contacts from each other.
Many mechanical switches fail over time from a problem known as contact erosion, which is the transfer of contact material from a first electrical contact to a second electrical contact. Contact erosion occurs just as two electrical contacts come together, and just as the two electrical contacts come apart.
Just as two electrical contacts come together, when the voltage across the two electrical contacts is large enough, the air in the gap between the two electrical contacts ionizes, and an electron current in the form of an arc flows from the electrical contact with the lower potential to the electrical contact with the higher potential.
The electron current instantly causes the two electrical contacts to melt and/or oxidize which, in the case of melting, results in a migration of the contact material, such as metal, from one electrical contact to the other electrical contact. In the case of the oxidization of the contacts, this will lead to contact resistance dependent on the conductance of the oxide and its thickness. The migration of material adds a contact resistance to the switch, and eventually leaves the first electrical contact without enough material to physically touch the second electrical contact, thereby leading to device failure.
In some applications, such as audio and video applications, the addition of a contact resistance to the switch can cause a significant deterioration in the signal that passes through the switch. In these cases, the contact resistance limits the effective lifetime of the switch to a period that is well less than the physical lifetime of the switch (when the two electrical contacts can no longer touch).
In a similar manner, just as the two electrical contacts come apart, when the voltage across the two electrical contacts is large enough, the current density increases dramatically. The increased current density melts the two electrical contacts which, in turn, results in a migration of the contact material from one electrical contact to the other electrical contact. As before, the migration of material adds a contact resistance to the switch, and leads to the eventual failure of the switch.
Thus, a contact resistance can develop when the switch opens as well as when the switch closes. As a result, there is a need for a mechanical switch that reduces the effect of contact resistance, thereby increasing the lifetime of the switch for applications which are sensitive to the addition of a contact resistance.